Biological decontamination and sterilization have a broad array of applications including medical equipment and device sterilization, food production and preservation, and preparation of consumer goods. Chemicals, heat, high-energy electron beams, and X-ray or gamma-ray irradiation systems are presently used for sterilization. Each of these systems has trade-offs due to the cost, efficiency, immobility, electric power requirements, toxic waste, personal hazard and the time required for sterilization or decontamination.
Plasmas have been used for decontamination and sterilization. Plasma, a fourth state of matter distinguished from gas, liquid and solid, may be produced through electrical discharge, for example electrical discharge through a gas. Although all plasmas contain electrons, ions and neutral species, they will have different properties depending on the composition of the gas used to prepare the plasma, as well as the electrical and structural configuration of the device used to produce the plasma.
One type of plasma is high-voltage cold plasma (HVCP), which may be prepared using dielectric barrier discharge (DBD) systems. HVCP may be prepared using non-equilibrium breakdown of a gas, using voltages preferably of 30 kV to 500 kV, typically at a frequency of 50 or 60 Hz with a DBD system. HVCP has not been studies as well as other types of plasmas, such as thermal plasma or RF plasmas. Consequently, there is presently no theory which explains the properties of these plasmas, nor the various excited and reactive species produced in such plasma. Over the last decade experimental examination of HVCP has been carried out to study this plasma.
Direct exposure of materials to HVCP has been studied. Of particular relevance are the studies exposing biological products and contaminants to HVCP, where the biological products are sealed inside packages and the HVCP is produced inside the package. In such studies, packaged foods such as produce and other materials were sterilized in a short period of time. The product inside the packages comes into direct contact with the plasma. Since the packages are sealed, reactive gas produced in the plasma remains in contact with the product indefinitely, is not diluted or dispersed, and the packaged product is protected from recontamination, dramatically extending the shelf life of the products, such as fruits and vegetables. See, for example, U.S. Pat. Pub., Pub. Nos. 2013/0189156 and 2014/0044595, both to Keener et al.